Iodinated X-ray contrast media (ICM) are commonly used in medical treatment facilities to image soft tissue in the human body. ICM have a global consumption rate of 3.5 x 10<sup>6</sup> kg per year and are excreted from the body 95% unmetabolized. ICM persist through conventional wastewater treatment processes, and therefore, can be found in surface waters at levels as high as 100 μg/L. Although ICM are non-toxic when ingested, previous studies have shown significant formation of toxic iodinated disinfection by-products (DBPs) in simulated chlorinated drinking water when ICM are present. Like drinking water, the majority of wastewater in the United States is also chlorinated. However, the potential formation of toxic iodinated DBPs from ICM in wastewater treatment and their impact on aquatic ecosystems has not been investigated. For this study, real wastewater samples across the state of Minnesota were analyzed to assess their cytotoxicity as well as quantify ICM and DBPs. ICM were quantified via liquid chromatography (LC)- tandem mass spectrometry (MS/MS) and priority, unregulated DBPs were quantified via gas chromatography (GC) -mass spectrometry (MS) using selected ion monitoring (SIM). Data reveal that ICM levels vary from river to river and that there are clear ICM hotspots. Further, samples collected over three years reveal that the concentration of iopamidol is temporally variable due to the patterns of usage at medical treatment facilities. Our studies have shown that these hotspots contain elevated levels of toxic I-THMs (iodo-trihalomethanes) and priority, unregulated DBPs in their treated wastewater effluents and downstream when compared to rivers with lower concentrations of ICM. Interestingly, recent sampling events have also shown an increase in nitrogenous disinfection by-products (N-DBPs) like haloacetamides and haloacetonitriles, which are more toxic than regulated trihalomethanes (THMs) and haloacetic acids (HAAs).

Role of iodinated X-ray contrast media as a source of iodine for the formation of iodinated DBPs upon chlorination at wastewater treatment plants

ACS Fall 2021

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